INTRAMURAL RESEARCH PROJECT Z01 DK 55101-01 MCEB October 1, 1997-September 30, 1998 Title of Project: Molecular Mechanisms of Thyroid and Nuclear Hormone Receptor Action Principal Investigator: P.M. Yen, M.D. (Investigator) MCEB, NIDDK, NIH Bethesda, MD 20892 Other Personnel: S. Ando, M.D. Ph.D. X. Feng, Ph.D. Y. Liu, M.A., M.D. P. Maruvada, Ph.D. P. Rotman, M.D. J. Palmer-East, B.A. Collaborating Units: None Staff-Years: 5.0 Human Subjects: Neither human subjects or tissues Summary of Work: Thyroid hormone receptors (TRs) belong to a superfamily of nuclear hormone receptors including the steroid hormone, vitamin D, and retinoid receptors. They can bind as heterodimers with retinoid X receptors to hormone response elements (HREs) located in the promoter region of target genes. For positively-regulated genes, thyroid hormone (T3) binds to the receptor and increases transcription. Interestingly, in the absence of T3, TRs can still bind to HREs and repress transcription below basal level. There is emerging evidence on how the receptor mediates these effects. Recently, several groups have described co-activators and co-repressors that interact with the receptor in a ligand- dependent manner. Additionally, there are other proteins that interact with the liganded receptor/co-activator complex such as CBP and p/CAF which have intrinsic histone acetylase activity. Similarly, co-repressors have been shown to complex with histone deactylases. Far-western and co-transfection studies from our group have suggested there are multiple proteins that can interact with both the unliganded and liganded TR. The identity of most of these proteins which form the receptor complexes which mediate transcriptional activation and basal repression still are not known. Our goal is to use techniques such as the yeast two-hybrid system and Far-Western analyses to identify nuclear proteins that interact with thyroid hormone receptors and steroid hormone receptors. We also plan to study the protein-protein interactions of identified co-factors with receptors using in vitro, cell culture, and histological approaches (particularly with green fluoroscent probes). We also will examine the interaction of these and previously described co-factors with natural mutant TRs from patients with thyroid hormone resistance syndrome. Additionally, in related work, we will study the action of mutant receptors in specific tissues (particularly adipose tissue) of transgenic mice which we previously have created. We also are targetting nuclear co-factors of thyroid hormone receptors to specific tissues in transgenic mice to understand their roles in vivo.